1. Field of the Invention
The present invention relates to communication networks. More particularly, the present invention relates to faulty station identification and isolation in a token ring network.
2. Art Background
Communication networks allow multiple computer systems, peripherals and other information storage, retrieval or processing units (stations) to share data. There are various network topologies that a communication network can adopt which are well-known in the art of communication networks; these topologies include the star topology, tree topology (or generalized bus topology) and token ring topology. In a token ring topology, units or nodes of the communication network are communicatively interconnected in a ring fashion with each node occupying a particular position within the overall ring structure. Several nodes on a particular ring may physically reside on a network concentrator which provides, among other control functions, a coupling platform for the associated nodes (stations). Each network concentrator of a Token Ring network may also contain a network management module which performs several control and timing functions for the nodes of the token ring network.
For one node to communicate with another node in a token ring network it must have priority to a unique token data frame or code which traverses the ring. This token travels around the ring until one node makes a request to communicate. The node wanting to communicate will take the token from the ring and transmit a signal indicating that the token is busy. When the token is busy none of the other nodes may communicate over the ring. The node with the token, the source node, may transmit a message package to another particular node, the destination node. The message package (data frame) will indicate the destination node by a particular label attached to the message. The message is passed along the nodes of the ring structure in a particular direction, node by node, until the destination node receives the message. After the destination node receives the message, it copies the message into an internal buffer and also continues to send the message along the ring until the source node receives the message back. When the source node receives its own message it releases the token back onto the ring and discontinues the message. A network management module (if one is present on the ring) may also remove messages that have traversed the ring more than once, i.e., if the source module faulted after sending the message.
In a token ring structure each node is called a repeater because each node repeats a message through the ring whether or not the message is destined for that node. Therefore, the communications scheme of a ring topology communication network requires that each and every node of the ring be operating properly to repeat messages around the ring. A disastrous effect will occur within a token ring network if one particular node or station malfunctions and will not repeat messages. A faulting station will break the communication line at that point. This occurrence will bring the entire token ring network down since messages will not flow past the malfunctioning node.
There are several potential causes for a node along a token ring to malfunction. First, a node having an incorrect communication frequency may be inserted into the token ring network. The incompatible frequency will lock out the newly added node from the network. Secondly, a cable may break between stations of the ring network thus breaking the ring at one or more places. If adjacent stations become physically isolated the network will fail. A station also may malfunction and not remove itself from the ring causing a break in the communication network. In any of a number of different scenarios, it would be advantageous to be able to detect a malfunctioning node and remove or isolate that node from the remainder of the network to prevent communication failure.
One method of identifying and isolating malfunctioning stations within the token ring system is to unplug cables associated with each station until the malfunctioning station is removed. This solution is not practical in large complicated network systems. Moreover, what is needed is a system that can automatically isolate the problem station without requiring user interaction. IEEE communication standard 802.5 provides a system for beacon removal within a communication network to prevent network shutdown. However, if the malfunctioning or problem station does not conform to the 802.5 standard then the malfunctioning station will not be removed from the ring network. What is needed is a system for identifying and isolating problem stations that do not conform to a particular standardized communication protocol.
U.S. Pat. Nos. 5,283,783 and 5,361,250 issued to Nguyen et al. and assigned to Bay Networks, Inc., of Santa Clara, Calif., each disclose an apparatus and method for token ring beacon station removal in a communication network wherein an intelligent agent controls the detection and isolation of faulty stations in the token ring network. The method and apparatus disclosed in those patents requires that the intelligent agent be one of the stations that is included in the token ring network. This is suitable in prior concentrators such as the System 3000.TM. family from Bay Networks, Inc., of Santa Clara, wherein if a given intelligent agent is present in the concentrator it will be included as a station in the affected network segment.
Modern network concentrators, such as the System 5000.TM. family from Bay Networks, Inc., of Santa Clara, Calif., support multiple token ring backplane buses within a single chassis. For example, the above-mentioned System 5000.TM. supports nine (9) backplane network segments which may be variably configured for organizing ports of host modules in different slots in the concentrator into different combinations of token ring networks. Additionally, host modules inserted within such a concentrator may themselves include local networks/segments. While a System 5000.TM. concentrator may include a network management module (NMM) such as the one described above, the NMM may not be configured to be a station on every token ring network segment associated with the concentrator. The teachings of the above two patents are suitable for detecting and isolating stations that are beaconing in a token ring network that includes the NMM as a station, but do not provide a solution for beaconing stations involved in a token ring in which the NMM is not a participating station. It would be desirable, and is therefore and object of the present invention, to provide a method and apparatus for faulty station identification and isolation for token ring networks in which the agent responsible for detecting and isolating beaconing stations is not itself a station in the token ring network.